In recent years, mobile terminal devices such as mobile phones have been equipped with various functions. Among such functions is a voice recording function with which voice information may be recorded, and may be played back and deleted as needed. However, since the memory capacity of a mobile terminal device is limited, there have been problems such as, when recording is performed while some important data have been recorded, the already-recorded important data were deleted.
In order to solve the problem, Patent document 1 discloses a mobile communication system in which a conversation being carried on with a mobile terminal device is recorded in a voice storage device disposed in a switching system so that the recorded content may be played back later to review the conversation content with the other party.
In addition, in relation to the above technique, Patent document 2 discloses a mobile phone that detects the memory usage rate, and performs message transfer of recoded digital signals to another phone having a recording function when the memory usage rate exceeds a predetermined level, in order to enable recording, playback etc. of a plurality of matters without increasing the memory capacity to be installed in the main body.
Patent document 1: Japanese Laid-open Patent Application No. 07-283873
Patent document 2: Japanese Laid-open Patent Application No. 08-223279